1. Field of the Invention
The present invention relates to an optical disc recording and playback apparatus that is configured so that a signal is recorded to disc by a laser emitted from an optical pickup and the signal recorded on the disc is played back by the laser.
2. Description of the Related Art
Disc players for reading signals that have been recorded on discs using optical pickups have become pervasive. In addition to the playback function, disc recording and playback apparatuses configured so as to enable signals to be recorded onto discs by a laser emitted from an optical pickup have become commercialized.
In an optical disc recording and playback apparatus, it is necessary to accurately aim the laser beam emitted from the optical pickup to a signal track on the disc surface, hence focus control and tracking control operations are performed. The related focus control operation is performed by supplying driving current to a focusing coil for displacing an objective lens toward the disc surface, and the tracking control operation is performed by supplying driving current to a tracking coil for displacing the objective lens in a radial direction on the disc.
Recently, the trend has been to increase the signal density so as to record more signals onto a disc. To increase the density, it is necessary to optimally aim the laser beam onto the disc. To perform this operation, an operation for correcting the relative angle of deviation between the disc and the objective lens, namely, an optical pickup configured so as to allow a tilt adjustment has been developed. (As an example, refer to Japanese Patent Laid-Open Publication No. 2002-197698.) A technique for detecting the tilt of the optical pickup with respect to the disc and for adjusting the tilt has also been developed. (As an example, refer to Japanese Patent Laid-Open Publication No. 2001-52362.)
The technique described in Japanese Patent Laid-Open Publication No. 2001-52362 comprises a tilt sensor for detecting the tilt of an optical pickup with respect to a disc and is configured to perform a tilt adjustment operation on the basis of a signal obtained from the tilt sensor. Although this technique is capable of performing accurate tilt control, the tilt sensor is expensive. This results in a problem where the optical disc recording and playback apparatus becomes expensive.
Furthermore, the tilt adjustment coil that is built into the optical pickup is fixed to a support member for supporting the objective lens. However, deviations in its installed position as well as changes in the ambient temperature, changes in the position of and deterioration from aging of the optical disc recording and playback apparatus result in the tilt angle not being constant while a driving voltage is not supplied to the tilt coil. Therefore, when the tilt adjustment operation is performed in this state, a problem arises in which an accurate tilt adjustment cannot be performed.